The season premiere of The Family Guy was even edgier than usual, exploring numerous alternate universes in an episode entitled "Road to the Multiverse." Resident genius toddler Stewie invents a device that enables him to travel between parallel universes with the family dog, Brian — who tries to pretend he knows about Many Worlds as Stewie explains the concept. It's a nice brief summary of the basic concept.
Soon Stewie and Brian are popping in and out of alternate universes: one that is far more technologically advanced than ours; one where everyone has two heads; one that is based on ironic Washington Post political cartoons; one that is completely Disneyfied, with cheery songs about pie and a touch of anti-semitism; and finally, a universe where dogs rule the world and humans are the pets. That's where Stewie meets his Dog Self and discovers he's had the device on "shuffle" all along — hence their random jumping around. Eventually they manage to get back to their reality, bringing Alternate Pet-Brian back with them — who [SPOILER ALERT!] is promptly hit by a bus, because after all, can two Brians co-exist in the same universe?
Scientists don't really know what would happen in such an instance. One of the critical features of most multiverse theories is that the various parallel worlds never interact. In fact, there's no direct evidence for the existence of a multiverse — and only a few proposals for how one might detect them if they did. For instance, we might see evidence of another bubble universe if it had collided with our own a long, long time ago — except such a collision would pretty much destroy the fabric of spacetime in both bubbles.
The latest scheme for evidence of a multiverse comes a new paper on the arXiv by Anthony Aguirre of the University of California, Santa Cruz, and Matthew Johnson, a postdoc at Caltech. They think they've come up with a version wherein spacetime in two alternative universes could be preserved, assuming they didn't so much as collide, as sideswipe — a sort of "cosmic scrape." Signs of a such a scrape would include a negative curvature to the universe, or the remnant patterns that could be observed in the cosmic microwave background. The latter has the advantage of possibly being detected from advanced telescopes. Even then, it would be a sliver of evidence, not definitive proof.
It's still tantalizing stuff. Maybe cosmologists in a technologically advanced parallel universe will beat us to it, and detect our presence first — inspired by their version of The Family Guy. Because if there's a mutliverse, there's got to be a version of Seth MacFarlane out there somewhere out there, too.